The present invention relates to a getter assembly for a gas discharge device.
Alkaline-earth materials, commonly barium, strontium, calcium, and titanium, may be used for "getters" which scavenge residual contaminant gases from rare earth gases such as helium and neon, as is known in the art. These getter materials are useful in the operation of gas discharge devices such as lasers which generally require a contamination-free mixture of rare earth gasses, e.g., helium and neon, to promote longer life.
In gas discharge devices employed as ring laser angular rate sensors, hereinafter referred to as ring laser gyros, a mechanically and thermally stable block provides a gas discharge cavity comprised of a plurality of interconnected tunnels and adjacent chambers. The gas discharge cavity provided by the laser block is evacuated and filled with helium and neon under low pressure. Commonly, two anodes and one cathode are symmetrically positioned along the optical closed-loop path in communication with the tunnels to provide a pair of ionization current paths, thereby creating counter-propagating laser beams. The gas discharge cavity of such ring laser gyros usually includes getter material for removing impurities from the helium-neon gas mixture.
In some ring laser gyros, the getter material is introduced in the gas discharge cavity by way of a getter assembly constructed of a getter pan suspended from a snap-ring via an extension member. The extension member is intended to advantageously position the getter pan assembly in close proximity to selected gas discharge cavity walls.
The getter pan is generally comprised of a metallic ring. The metallic ring generally includes a trough or depression therein which is filled with getter material, thereby providing what is referred to as the getter pan. In turn, the getter pan is secured to the snap-ring by welding one end of the extension member to the getter pan, and the other end of the extension member is welded to the snap-ring. Alternatively, the getter pan may be welded directly to the snap-ring.
The snap-ring resembles common fastener-type snap-rings. Two holes symmetrically located at the ends of the snap-ring are provided to facilitate positioning of the getter assembly within one of the aforementioned chambers within the gyro block. A tool similar to a needle-nosed pliers is inserted into the holes of the snap-ring and operated to compress the snap-ring. In turn, the snap-ring with getter pan is positioned inside of a chamber within the gyro laser block. The tool is then removed which in turn allows the snap-ring to place the extremities thereof in outward tension against the gas discharge cavity walls thereby holding the getter assembly firmly in position within the gas discharge chamber.
After the injection of a helium-neon gas mixture into the laser block, the gas discharge cavity is closed off at its gas-filling pinch tube, leaving the getter assembly inside the gas discharge cavity chamber. Next, the getter pan is inductively heated by means of external coils. The heat transferred from the getter pans, in turn, heats the getter material residing therein to its flash point. Flashing the getter effectively vaporizing the getter material and results in a deposition of a film of activated getter material on portions of the gas discharge cavity walls, particularly in the chamber holding the getter assembly.
The getter assembly described above has several disadvantages. After the getter has been flashed, particulate getter material from the getter pan may also shed from the pan due to shock and/or vibration encountered by the ring laser gyro. This particulate getter matter contaminates the cavity and reduces the useful life of the laser. Also, shock and vibration may cause the getter pans to oscillate, which stresses the weld joints at the ends of the extension member. Further, getter pan vibration oscillations stir up the gas mixture in the cavity which may impact bias instability in ring laser gyros.